Generally a DCR of something below 9:1 is what many engine builders use as a cut off point for pump fuel (not talking E85 here), so I wouldn't argue with your figure of 8.75:1 DCR.

That said, in boosted applications there are ways to fight detonation besides lowering the CR or timing as I'm sure you're aware- water/alky injection, air-to-air or to water intercoolers, N2O cooled intercoolers, boost retard, to name a few.

To run a boosted engine at anything approaching optimum timing w/a DCR that are above what is known to cause detonation is going to require better fuel than you can buy from most pumps along w/one or more of the schemes mentioned above, I just don't see any practical way around it.

BTW, unless you actually saw an engine go together, there's no way the CR can be verified as being xx:1, IMHO. Guys have been known to exaggerate, you know... not saying anyone's pulling your chain, just sayin'.